1. Field of the Invention
The present invention relates to a device for supporting a specimen holder used in an electron microscope.
The specimen holder extends through the outer wall member of the electron microscope or other instrument whose interior is maintained as a vacuum. The specimen holder is slidable inwardly and outwardly. Atmospheric pressure urges the specimen holder inward and applies pressure to a member bearing against the inner end of the specimen holder. The supporting device in accordance with the invention is used to alleviate the pressure applied to this member.
2. Description of the Related Art
The aforementioned device for supporting the specimen holder is known as shown in FIGS. 13 and 14. FIG. 13 is a schematic cross-sectional view of this known supporting device. FIG. 14 is a cross-sectional view taken on line XIVxe2x80x94XIV of FIG. 13.
For ease of understanding of the following description, the forward and rearward direction is taken as the X direction. The horizontal direction is taken as the Y direction. The vertical direction is taken as the Z direction. The direction indicated by the arrow X is the forward direction. The direction indicated by the arrow xe2x88x92X is the backward direction. The direction indicated by the arrow Y is the rightward direction. The direction indicated by the arrow xe2x88x92Y is the leftward direction. The direction indicated by the arrow Z is the upward direction.
The direction indicated by the arrow xe2x88x92Z is the downward direction.
The direction indicated by symbol {circumflex over (.)} is a direction directed from the rear side of the plane of the page to the front side. The direction indicated by symbol {circumflex over (x)} is a direction directed from the front side of the plane of the page to the rear side.
In FIGS. 13 and 14, the microscope column of an electron microscope is generally indicated by 01 and has a yoke 02 made of a magnetic material and a substantially cylindrical goniostage Gs made of a nonmagnetic material. The yoke 02 has a cylindrical outer surface. The goniostage Gs is held inside the yoke 02. The yoke 02 forms a part of the outer wall of the microscope column 01.
Referring next to FIG. 14, the yoke 02 supports an excitation coil 04, a top magnetic polepiece 06 of an electron lens, and a bottom magnetic polepiece 07 of the electron lens. The polepieces have electron passage holes, respectively. A specimen chamber A is formed between the magnetic polepieces 06 and 07 of the electron lens inside the gonistage Gs.
The yoke 02 and the goniostage Gs are provided with goniometer-receiving holes 02a and Gs1, respectively, on the xe2x88x92X side as viewed in FIGS. 13 and 14. The holes 02a and Gs1 place the outside of the yoke 02 in communication with the specimen chamber A. The yoke 02 and the goniostage Gs are formed with positioning member-receiving holes 02b and Gs2, respectively, on the X side as viewed in FIGS. 13 and 14. The holes 02b and Gs2 place the outside of the yoke 02 in communication with the specimen chamber A.
A goniometer Gm is mounted in the goniometer-receiving holes 02a and Gs1, and supports a specimen holder H extending from outside the yoke 02 into the inside specimen chamber A.
The specimen holder H has a holder grip H1 at its outer end to permit an operator to operate the specimen holder. The holder H has an elongated specimen-holding portion H2 at its inner end. The specimen holder H is provided with an O-ring groove in which an O-ring H3 is accommodated. A guide pin H4 (see FIG. 14) is mounted on the outer surface of the specimen holder H.
The goniometer Gm has a cylindrical bearing 08 and a cylindrical support member 09 fixedly mounted in the goniometer-receiving holes 02a and Gs1, respectively. A spherical bearing 09a is formed at the inner end of the support member 09. The cylindrical bearing 08 has a cylindrical inner surface on which bearings 011 are mounted. The cylindrical bearing 08 is so disposed that the axis of its cylindrical inner surface extends horizontally and passes through the center O of the spherical surface of the support member 09.
The goniometer Gm has a rotatable member 012 and a holder mounting member 013. The rotatable member 012 is held by the bearings 011 so as to be angularly adjustable around the X-axis.
The holder mounting member 013 is provided with a hole 013a extending therethrough to hold the specimen holder H. The outer surface of the inner end of the holder mounting member 013 forms a spherical surface 013b. The holder mounting member 013 is held by the spherical bearing 09a so as to be angularly adjustable around the center O of the spherical surface. The hole 013a extending through the holder is coincident with the X-axis at a reference position.
Referring to FIG. 14, a Z-direction positioning drive mechanism (hereinafter referred to as the Z-positioning drive mechanism) Dz is mounted at the bottom of the outer-end portion (on the xe2x88x92X side) of the rotatable member 012. If the holder mounting member 013 is rotated in the Z direction by the Z-positioning drive mechanism Dz, the position of the inner end of the specimen holder H in the Z direction can be adjusted.
Referring to FIG. 13, a Y-positioning drive mechanism Dy is mounted to a right-side portion of an outer-end portion (on the xe2x88x92X side) of the rotatable member 012. The position of the inner end of the specimen holder H in the Y direction can be adjusted with the Y-positioning drive mechanism Dy. The position of the inner end of the specimen holder H in the Y direction is detected by a Y-linear gauge Ly in contact with the outer surface of the holder mounting member 013.
In FIGS. 13 and 14, a positioning drive mechanism support member 016 is fitly mounted in the positioning member-receiving hole 02b formed on the X side of the yoke 02 and goniostage Gs. A slider-receiving hole 016a and a lever-receiving hole 016b lying on the X-axis are formed in the positioning drive mechanism support member 016. A holder inner end-positioning drive mechanism Dx (see FIG. 14) has a positioning slider 017 that is received in the slider-receiving hole 016a so as to be adjustable in the X direction.
Referring to FIG. 14, the holder inner end-positioning drive mechanism Dx has a lever 018, a lengthwise position-adjusting screw 019, and a lengthwise position-adjusting motor 021.
In FIGS. 13 and 14, the lever 018 is held in the lever-receiving hole 016b formed in the positioning drive mechanism support member 016 so as to be rotatable about the Y-axis. One end of the lever 018 abuts against the outer end (on the X side) of the positioning slider 017. The other end of the lever 018 abuts against the front end (on the xe2x88x92X side) of the lengthwise position-adjusting screw 019. As shown in FIG. 14, as the lengthwise position-adjusting motor 021 is rotated, the lengthwise position-adjusting screw 019 is moved forward or rearward via an output gear 022 and via a gear 023 of the holder inner end-positioning drive mechanism Dx, thus moving the end of the lever 018 in the X direction.
A member 024 for placing the inner end of the holder inner end-positioning drive mechanism Dx in position is located in the positioning member-receiving hole Gs2 formed in the goniostage Gs. The inner end of the specimen holder H and the inner end of the positioning slider 017 bear against the inner end-positioning member 024. This inner end-positioning member 024 determines the position of the inner end (on the X side) of the specimen holder H. and is held by the goniostage Gs so as to be movable within a quite narrow range. The amount of movement of the specimen holder H in the X direction is detected via the inner end-positioning member 024 and via the lever 018 by an X-linear gauge Lx (see FIG. 14) in contact with one end of the lever 018.
With the prior art technique described above, the specimen-holding portion H2 at the inner end of the specimen holder H is urged to bear against the holder inner end-positioning drive mechanism Dx by atmospheric pressure (back pressure), the drive mechanism Dx being on a vacuum side. Thus, pressure is applied to the holder inner end-positioning drive mechanism Dx.
Because of this pressure, force tends to stay in the components of the holder inner end-positioning drive mechanism Dx if there is slight resilient deformation or displacement. Therefore, the specimen-holding portion H2 of the specimen holder H tends to creep during observation, causing xe2x80x9cafter driftxe2x80x9d of the specimen held on the specimen-holding portion H2 during observation.
With the prior art technique described above, the amount of movement of the specimen holder H in the X direction is detected via the holder inner end-positioning drive mechanism Dx in which force tends to stay as described above. Therefore, the detection accuracy is poor. Especially, the member 024 for placing the inner end of the holder inner end drive mechanism Dx in position is held by a spring, and is displaced according to displacement of the specimen-holding portion H2. Consequently, the position detection accuracy in the X direction tends to deteriorate.
It is an object of the present invention to provide a specimen holder support device acting to support a specimen holder extending through an outer wall forming a chamber maintained as a vacuum such that the specimen holder is slidable, the specimen holder support device having a holder inner end-positioning drive mechanism for placing the inner end of the specimen holder in position, the specimen holder support device being characterized in that pressure applied to the holder inner end-positioning drive mechanism by atmospheric pressure (back pressure) via the specimen holder is alleviated. The specimen holder support device is further characterized in that the position of the specimen holder in the axial direction is detected accurately.
This object is achieved in accordance with the teachings of the present invention by a specimen holder support device that is for use with an electron microscope having a specimen chamber defined by a wall, the specimen holder support device comprising a cylindrical support member extending through the wall of the chamber and mounted to this wall, a swinging member inserted in the support member, a specimen holder slidably mounted in the swinging member via an O-ring, and an X-motion drive mechanism engaging the front end of the specimen holder. A spherical bearing is formed on the inner surface of the support member. The swinging member can swing about the spherical bearing in the Y- and Z directions. This specimen holder support device is characterized in that there is provided a holder movement-limiting means for reducing force applied to the X-motion drive mechanism from the specimen holder.
Other objects and features of the invention will appear in the course of the description thereof, which follows.